The present disclosure relates generally to semiconductor manufacturing. Specifically, the present disclosure relates to systems and methods that write to a medium using electron beams.
Electron-beam (or “e-beam”) writing relates to a process for creating changes in a medium using e-beams. Specifically, some e-beam processes use e-beams to write designs onto mediums. Examples of mediums that can be written on with e-beams include semiconductor wafers and photomasks (e.g., fused silica and chrome masks). E-beam writing provides a way to create features on a medium where the features are smaller than a resolution limit for light.
Some conventional systems use a single-beam method to write designs to a photomask. In one conventional system, in order to mitigate the beam-stitching effect, multiple passes are made by a single beam to apply the desired dosages to the medium. Dosage refers to the amount of electron beam exposure at a given point or area, e.g., e-beam current multiplied by exposure time at a given area is a way to measure dosage. Assuming that the beam is kept at a constant current, dosage increases with a number of passes over an area. Furthermore, throughput is typically inversely proportional to dosage applied by a particular pass. Single-beam exposure methods may be undesirably slow for some applications; thus some applications are evolving to a massive beam exposure technique.
Conventional massive beam exposure techniques employ a single source with multiple apertures to generate parallel beams, where each of the parallel beams are individually controllable as to placement, size, dose, and blur. Also, the beams can be individually calibrated. In one conventional technique, a set of parallel beams are used to write parallel strips on a medium simultaneously. The beams are moved in the x-direction by deflection and in the y-direction by scanning movement of the medium to make a zigzag movement to apply a desired dosage and create the parallel strips.
However, one issue with conventional massive beam techniques is beam-to-beam variation, and without some way to ameliorate beam-to-beam variation, one or more of the strips may be different from other strips and/or deviate from the desired dosage. Precise calibration for all beams can be difficult, so some conventional techniques account for beam-to-beam variation by overlapping the writing zones between adjacent beams. The overlapped writing zones are referred to as stitches, and while not considered part of the strips, stitches are used to average beam-to-beam variation between adjacent beams.
The massive beam techniques can use Gaussian beams, where each beam is a single beam, or patterned beams, where each beam includes a set of sub-beams that are not individually controllable and are arranged in an array.
The above-described conventional techniques have some disadvantages. For instance, as mentioned above, techniques using single beams with multiple passes may be undesirably slow, i.e., throughput may not be high enough for some applications. Also, some conventional massive beam techniques using stitching may find throughput negatively affected by the time used to write in the overlapped areas. More efficient and effective e-beam writing is called for.